The present invention relates to a Multiple Sub-Nyquist Sampling Encoding hereinafter called as MUSE/NTSC standard converter for converting a HDTV broadcasting being transmitted with MUSE standard to be watched through the present NTSC standard television set, and particularly to a converter for converting a picture screen of HDTV having aspect ratio of 9 to 16 into that of the present television having aspect ratio of 3 to 4.
In converting a picture screen of a HDTV having aspect ratio of 9 to 16 into that of the present TV having aspect ratio of 3 to 4, the zoom-up mode conversion method and a wide mode conversion method have been used.
In converting into a zoom-up mode, both sides of a picture screen of HDTV is cut off on the order of 30% and only 70% of center is converted to be watched through NTSC standard TV. In converting into a wide mode, a HDTV video image having aspect ratio of 9 to 16 is entirely watched in a picture screen of NTSC standard TV having aspect ratio of 3 to 4 and at the same time, the portion of which video image is not exist in the upper and lower part on a NTSC standard picture screen is watched on the order of 28.6%.
As shown in FIG. 1, a MUSE/NTSC standard converter according to the prior art primarily converts a HDTV video image of 1125 lines into video image of 525 lines using a vertical interpolation filter for a zoom-up mode in order to provide both of a zoom-up mode conversion in which both sides of a picture screen of HDTV is cut off on the order of 30% and only 70% of center is converted to be watched through NTSC standard TV and a wide mode conversion in which a HDTV video image having aspect ratio of 9 to 16 is entirely watched in a picture screen of NTSC standard TV having aspect ratio of 3 to 4 and at the same time, the non-marked portion is exist on the order of 28.6% in the upper and lower part on a NTSC standard picture screen.
Secondarily, the picture screen converted into 525 lines is interpolated using a vertical interpolation filter for a wide mode and then vertically compressed into the 350 lines, thereby generating a picture screen converted into a wide mode.
As aforesaid, the MUSE/NTSC standard converter according to the prior art has disadvantages as follows.
Because both of vertical interpolation filters for a zoom-up mode and for a wide mode are used, hardware is increased in quantity. If a picture screen of 1125 lines is directly converted into that of a wide mode, said picture screen having 1125 lines can be converted into that of 375 lines by reducing 1125 lines by a third. However, if a picture screen of 525 lines is converted into that of 350 lines, it is converted by reducing 525 lines by two-third so that a vertical resolution is degraded approximately on the order of 7.5%.
Aforesaid mode conversion technique-is disclosed in more detail in Japanese Laid Open Patent Application No. 89-292984.